多孔介质中甲烷水合物的生成特性研究进展

天然气水合物是一种清洁高效的能源,常常在自然界中的海底沉积物多孔介质孔隙中生成,同时水合物在工业上还能与多孔介质材料一起作为储存及分离气体的一种方式,因此开采利用水合物以及发挥水合物工业技术的前提都跟多孔介质有莫大的关系,对多孔介质中天然气水合物生成特性的研究进行总结与分析具有非常重要的意义。本文总结分析了国内外关于不同类型多孔介质中甲烷水合物的生成过程及特性的研究文献,将多孔介质根据其孔径大小进行划分。结果显示,在微孔介质中,甲烷水合物的生成侧重于气体的存储及运输方面;在介孔介质中,甲烷水合物的生成动力学受孔径影响较大;在大孔的沉积物中,甲烷水合物的生成及分布的机理性研究仍比较缺乏。因此,需要进一步的研究来丰富甲烷水合物在多孔介质中的生成动力学理论,本文将在文献调研的基础上为今后的研究方向提出一些展望和思路。     

多孔介质中甲烷水合物的微观分布对电阻率的影响

电阻率测井技术是天然气水合物储层资源量估算的重要手段,明确储层电阻率与水合物在沉积物孔隙中微观分布的关系对准确估算水合物饱和度有重要意义。使用自主研发的天然气水合物计算机断层扫描（CT）技术-电阻率测量装置,开展多孔介质中甲烷水合物生成实验,同时进行CT观测与电阻率测试,得到了反应过程中扫描图像和电阻率数据,讨论了孔隙中水合物在不同微观分布模式下电阻率与水合物饱和度的关系。结果表明：水合物饱和度低于10.50%时,水合物以接触分布模式为主,与水合物对孔隙的填充效应相比,排盐效应更加显著,电阻率随水合物饱和度增大略有下降;水合物饱和度为10.50% ~ 22.34%时,水合物为悬浮与接触共存分布模式,悬浮分布模式下的水合物对孔隙水连通截面的阻塞作用较大,电阻率随水合物饱和度的增大急剧升高;水合物饱和度为22.34% ~ 27.50%时,水合物仍然为悬浮与接触共存分布模式,在大部分孔隙已被堵塞的情况下水合物的填充作用对电阻率影响较小,电阻率随水合物饱和度增大而升高的趋势逐渐变缓。可见,电阻率响应特性在不同的水合物饱和度范围下明显不同,与水合物的微观分布有关。     

含内热源可燃性多孔介质中的传热研究

煤粉、弹药等含内热源的可燃性多孔介质传热过程在自然界和工程中广泛存在。文中分析了可燃多孔介质的热传递机理，建立了相应的导热计算模型，给出了典型物种在内热源作用下的内部温度场。     

天然气在渐变型多孔介质中的预混燃烧

设计了孔径沿程变化的渐变型多孔介质(GVPM)燃烧器，为了解天然气在其中的预混燃烧特性，对燃烧室气体、固体温度分布和CO、NO；污染物排放进行了测量．试验研究了渐变型多孔介质中燃烧的温度场分布、火焰移动、污染物排放、稳定性及多孔介质孔径结构对燃烧特性的影响规律．将研究结果与几种均匀型多孔介质(HPM)中的燃烧进行比较，发现渐变型多孔介质中的燃烧可以有更多的优点，包括均匀温度场分布、极低污染物排放、高火焰速度、高稳定性、宽燃烧极限和有很大的负荷调节范围等．     

多孔介质内甲烷水合物生成动力学研究

天然气水合物作为一种潜在的新型潜在替代能源,分布广泛、储量巨大。水合物生成动力学特性对于了解自然界天然气水合物形成规律与水合物相关技术应用具有重大意义。针对甲烷水合物生成动力学特性进行研究,设计开发了甲烷水合物生成测试系统,研究了不同温度和不同孔隙粒径的多孔介质对于水合物生成动力学的影响。结果表明,随着温度的降低以及多孔介质孔隙粒径的减小,甲烷水合物生成过程中的气体消耗速率越快,生成结束时消耗的气体的量越多。同时,利用水合物生成多步骤机制模型,获得了甲烷水合物生成过程各中间产物的变化规律。     

凝析油气在多孔介质中的相态研究进展

凝析油气体系在地层多孔介质中的储存和渗流，与储层多孔介质形成一个相互作用的系统。多孔介质中的毛管压力、吸附作用、润湿性等必然对油气相态特征和渗流规律有一定程度的影响；尤其在低渗透多孔介质中，影响更为严重。本文对油气在多孔介质中的相态变化规律进行了系统的阐述，比较了流体在有多孔介质和无多孔介质时的相态特征。     

等温容器内多孔介质强化导热研究

等温容器是在充放气过程中容器内温度基本保持不变的一种特殊容器,在气动系统中有着广泛的应用.为强化放气过程中容器壁向内部的导热,以容器截面为研究对象,对内部铜丝的分布进行了探讨.在细铜丝填充密度一定的情况下,基于多孔介质模型,以容器截面导热热阻最小为目标,优化出两层和三层变密度填充下金属丝的分布.其热阻与均匀填充时相比,分别减少了37.63%和43.70%.研究结果表明,通过改变等温容器内细铜丝的分布可以强化容器壁向内部的导热.     

多孔介质燃烧的研究进展与应用

阐述多孔介质燃烧的原理,总结燃烧、流动和多孔介质材料对燃烧效果的影响,介绍该热点问题的研究进展,并对其应用前景作以介绍.     

多孔介质中的相变传热特性及其在建筑物节能中的应用

将非饱和多孔介质应用于建筑节能，使低品位，低密度的太阳能通过工质的相变得以利用，对实现建筑物的采暖具有应用价值。通过对非饱和多孔材料内的二维流场，温度场以及蒸发量场的数值计算，分析了两端开口的圆柱环型多孔腔内非饱和多孔介质的传热传质特性，研究了流体雷利数及边界条件的变化对多孔床热质迁移的影响。     

惰性多孔介质内天然气预混燃烧的数学模拟评述

天然气在惰性多孔介质内的预混燃烧是一个包含燃烧、辐射、对流及导热的复杂过程，从数学模拟的角度，比较了几种不同的甲烷-空气化学反应模型，研究了多孔介质内辐射传递方程的不同求解方法，并且分析了多孔介质的导热系数、对流换热系数等对燃烧器性能的影响。     

A thermal dispersion model for single phase flow in porous media

A new model for thermal dispersion is proposed based on the character of flow in porous media which relates the dispersion with the velocity and the tortuosity of fluid flow in the pores. Compared with former similar models, this one has fewer adjustable empirical constants, and therefore it is expected to be used more conveniently. The prediction by the present model can successfully reproduce the temperature distributions in the nearby wall region when a single phase fluid flows through a packed channel. The results of Nu versus Re agree well with the experimental results. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(6): 545–552, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10107     

Experimental measurements and numerical computation of nanofluid and microencapsulated phase change material in porous material

The electronic industry is increasingly investigating different approaches for the cooling of electronic equipment. The use of bulk phase change materials is also a promising approach for energy storage. The introduction of microencapsulated phase change materials combined with nanofluids can be beneficial. The combined use of a nanofluid and a metallic porous material can be used to mitigate problems resulting from small thermal conductivity. This study investigated a ternary mixture of water with a nanofluid and a microencapsulated phase change material in a porous medium. The model was previously validated with experimental data using a 0.5%vol concentration nanofluid in water. The results revealed that heat storage capability can be achieved as long as the microencapsulated phase change materials, which consists of encapsulated eicosane, is at a concentration of 20%. Because the melting temperature of microencapsulated phase change materials is approximately 36^°C , energy storage at a low flow rate and heat flux is recommended.     

Mixed convection in porous media between vertical concentric cylinders

In this paper, the dimensionless parameters Gr^**/Re_p and H/d_p that govern mixed convection in a vertical annulus filled with porous media, are deduced through dimensional analysis, and the criteria for mixed convection is established thereby. The calculated results for detecting the non-Darcian effects are discussed. The predictions agree with the experiments. © 1999 Scripta Technica, Heat Trans Asian Res, 28(2): 95–101, 1999     

Study on effective thermal conductivity for porous media using fractal techniques

In this paper, the geometric structure of porous media is described using fractal techniques, and a section particle area fractal dimension d of a porous medium with various porosities is considered with a simplified model. Also an expression of the effective thermal conductivity for soil is presented via a fractal dimension and a model of heat transfer in soil. The results obtained in this paper indicate the effectiveness of the method for determining the effective thermal conductivity by using the section area dimension. © 2000 Scripta Technica, Heat Trans Asian Res, 29(6): 491–497, 2000     

Determination of Effective Thermal Conductivity ForReal Porous Media Using Fractal Theory

INTRODUCTIONPorousmediaisacompositemediathatincludessolidframeandfluidandexistedwidelyintheeajrthbiosphere.Heatandmasstransferinporousmediaisbothanaturalphenomenoninearthbiosphereandaphysicalchemistryprocessinindustries,agricultureandhumanlife.Thusthestudyonheatandmasstransferinporousmediahasbecomeanimportanttasktoscielltistsandengineers.Heatandmasstransferinporousmediaisaverycomplexobject.Therearestillmanydifficultiestodescribethecoupledheatandmasstransferphenomena.Amongthesedifficultie…     

多孔介质中预混火焰猝熄及自稳定性研究

分析了多孔介质中预混火焰的猝熄效应,试验测定了一系列工况下泡沫陶瓷的猝熄直径和自稳定范围,为多孔介质燃烧器的开发设计提供了依据。通过分析发现,猝熄直径受到多个参数的影响,包括：混合气体的流速u、预混气体的层流火焰传播速度SL、燃烧室空管Re、预混气体的导温系数a、当量比φ以及多孔介质固体温度Ts。通过对多孔介质中燃烧的自稳定性试验研究,发现了多孔介质燃烧器中火焰稳定极限(吹脱极限和回火极限)与多孔介质平均孔径和气流速度及燃烧当量比的关系。     

Experimental study on the two phase flow behavior in PEM fuel cell parallel channels with porous media inserts

In this study, the air–water two phase flow behavior in PEM fuel cell parallel channels with porous media inserts was experimentally investigated using a self-designed and manufactured transparent assembly. The visualization images of the two phase flow in channels with porous media inserts were presented and three patterns were summarized. Compared with the traditional hollow channel design, the novel configuration featured less severe two phase flow mal-distribution and self-adjustment to water amount in channels, although a higher pressure drop was introduced due to the porous media inserts. The dominant frequency of pressure drop signal was found to be a diagnostic tool for water behavior in channels. The novel flow channel design with porous media inserts may become a solution to the water management problem in PEM fuel cells.     

Heat transfer of phase change materials (PCMs) in porous materials

In this paper, the feasibility of using metal foams to enhance the heat transfer capability of phase change materials (PCMs) in low- and high-temperature thermal energy storage systems was assessed. Heat transfer in solid/liquid phase change of porous materials (metal foams and expanded graphite) at low and high temperatures was investigated. Organic commercial paraffin wax and inorganic calcium chloride hydrate were employed as the low-temperature materials, whereas sodium nitrate was used as the high-temperature material in the experiment. Heat transfer characteristics of these PCMs embedded with open-cell metal foams were studied. Composites of paraffin and expanded graphite with a graphite mass ratio of 3%, 6%, and 9% were developed. The heat transfer performances of these composites were tested and compared with metal foams. The results indicate that metal foams have better heat transfer performance due to their continuous inter-connected structures than expanded graphite. However, porous materials can suppress the effects of natural convection in liquid zone, particularly for PCMs with low viscosities, thereby leading to different heat transfer performances at different regimes (solid, solid/liquid, and liquid regions). This implies that porous materials do not always enhance heat transfer in every regime.     

Non—Darcian and Anisotropic Effects on Natural Convection in Horizontal Porous Media Enclosure

Natural convection heat transfer in a horizontal enclosure filled with anisotropic porous media,being isothermally heated at bettom and cooled at top while the vertical walls being adiabatic,is numerically studied by applying the Brinkman model-a modified form of Darcy model giving consideratioin to the viscous effect.The results show that:(1)a larger permeability ratio(K^*) causes a lower flow intensity in the enclosure and a smaller Nusselt number,all Nusselt numbers approach unity in the limit of K^*→∞;a larger thermal conductivity ratio(λ^*) causes a stranger distortion of isotherms in the enclosure and a higher flow velocity near the walls,all the Nusselt numbers approach unity in the limit of λ^*-→0,the permeability and thermal conductivity ratios generally have opposing effects on the Nusselt number.(2) an increasing Darcy number decreases the flow intensity and heat tansfer rates,which is more significant at a lower permeability ratio.In particular,with K^*≤0.25,the Nusselt number for Da=10^-3 would differ from that of Darcy flow up to an amount of 30%,an analysis neglecting the non-Darican effect will inevitably be of considerable error.     

Investigation of moisture transfer mechanism in porous media during a rapid drying process

In this work, the moisture transfer mechanism in wet porous media during a rapid drying process was investigated experimentally and analytically. By means of scanning electron microscopy, the rapid drying processes for potato, carrot, and radish species were observed and recorded. A new displacement model using the pressure gradient in a porous material during rapid drying was suggested. To analyze this displacement flow in a porous material, the variables of this flow in a single capillary tube, such as velocity, flow rate, as well as the displacement time of internal moisture, were calculated. © 2000 Scripta Technica, Heat Trans Asian Res, 30(1): 22–27, 2001